A pilot study to determine whether a modification to electrodes used in iontophoretic cystic fibrosis sweat tests should be considered. Replacement of standard copper electrodes with carbon impregnated rubber electrodes is evaluated in an attempt to improve electrode to skin electrical interface. Rubber electrode characteristics were tested in vitro revealing no contra indications for CF sweat test utilization. In vivo tests are required to: first, assure reproducibility of copper electrode test results after substitution with rubber electrode; second, determine whether level of discomfort produced by the test is altered; and third, determine whether burns may be likely with the test electrodes. Adult subjects, rather than pediatric diagnostic population, are required for purposes of safety and research logistics.